1. Field of the Invention
The present invention relates generally to a chain guide adapted to be mounted to a mount surface of an engine block, for example, for guiding the travel of a chain, and more particularly to an improvement in and relating to a joining structure between a guide shoe and a guide base of the chain guide.
2. Description of the Related Art
Conventionally, in a chain transmitting apparatus used in an automobile engine, as shown in FIG. 6 hereof, a chain A4 is trained around a drive sprocket Al and two driven sprockets A2 and A3, and a chain guide A5 is disposed on an exterior side of a longitudinal portion of the chain A4 which constitutes a tension run (also called "tension side") of the chain A4.
The chain guide A5 has a function to suppress vibrations of the chain A4 while running, in cooperation with a tensioner device A6 which is disposed on the exterior side of a slack run (also called "slack side") of the chain A4 to remove a slack of the chain A4.
The conventional chain guide A5 is generally composed of a guide shoe A7 formed from a synthetic resin and having a shoe surface S adapted to be held in sliding contact with the rear surface of each plate P of the chain A4 (i.e., an outer circumferential surface of the chain A4), and a guide base A9 made of metal and firmly secured by a plurality of bolts A8 to a mount surface of an engine block, for example, of the automobile engine.
As shown in FIG. 7, the guide shoe A7 includes a plurality (two being shown) of pairs of hook-shaped locking prongs A10 arranged along opposite longitudinal edges of the guide shoe A7 at longitudinal intervals. The locking prongs A10 project perpendicularly from a rear surface of the guide shoe A7 which is opposite to the shoe surface S. The guide shoe A7 further has a pair of locking portions A11 and A12 provided at both longitudinal ends of the guide shoe A7 thereof (which correspond to a forward end and a backward end of the guide shoe A7 when viewed from the direction of travel of the chain A4, as shown in FIG. 6). The locking portions A11, A12 are engageable with forward and backward ends of the guide base A9.
The guide base A9 is made of metal and has a plurality of pairs of recessed portions A13 formed in opposite side surfaces (upper and lower surfaces) of the guide base A9 at a position corresponding to the position of the locking prongs A10 for receiving therein respective pairs of the locking prongs A10.
Mounting flanges A14 project from both longitudinal ends of the guide base A9 in a direction toward an inner circumferential surface of the chain A4 (FIG. 6). The mounting flanges A14 have bolt holes h formed at the same pitch as threaded holes (not shown) formed in the mount surface of the engine block. The bolts A8 extend through the holes h in the mounting flanges A14 and are threaded into the threaded holes in the mount surface to fasten the guide base A9 to the mount surface of the engine block, as shown in FIG. 6.
The conventional chain guide A5 of the foregoing construction is assembled as follows. While the locking prongs A10 of the guide shoe A7 are held in alignment with the corresponding recessed portions A13 of the guide base A9, the guide shoe A7 is pressed or forced toward the guide base A9. Forward movement of the guide shoe A7 relative to the guide base A9 causes the opposed locking prongs A10 to spread out against the resiliency thereof until front locking noses T (FIG. 8) of the locking prongs A10 move into a corresponding pair of recessed portions A13 of the guide base A9. Continuing forward movement of the guide shoe A7 causes the front locking noses T of the locking prongs A10 to project from a rear surface B of the guide base A9 whereupon the locking prongs A10 are allowed to spring back to restore their original shape. Thus, the locking noses T of the locking prongs A10 are interlocked with the rear surface B of the guide base A9 to thereby assemble together the guide shoe A7 and the guide base A9, as shown in FIG. 8. At the same time, the locking portions A12 (FIG. 7) provided at the forward and backward ends of the guide shoe A7 are brought into abutment with the forward and backward end faces of the guide base A9 to thereby position the guide shoe A7 relative to the guide base A9.
In the conventional chain guide A5 shown in FIGS. 6 through 8, since the mounting flanges A14 of the guide base A9 are bolted to the mount surface of the engine at a side adjacent to an inner circumferential surface of the chain A4, a free space defined by the inner circumferential surface of the chain A4 can be used efficiently.
However, since one locking prong of each pair of locking prongs A10 is inserted between the mount surface E (FIG. 8) and a lower surface of the guide block A9, it is practically impossible to integrate the two mounting flanges A14 into a single, relatively large mounting flange. Additionally, due to the presence of the recessed portions A13 formed in the guide base A9 for receiving therein the locking prongs A10 of the guide shoe A7, the guide base A9 is structurally weakened at such recessed portions and hence stiffness and rigidity of the guide base A9 are relatively low. Accordingly, while the chain A4 is traveling, the guide base A9 tends to vibrate in resonance with the chain A4, thus forming a source of undesired vibration and noises.
In view of the foregoing problem, an attempt has been made to provide a guide base with a single mounting flange designed to extend along the entire length of the guide base for the purpose of increasing the mechanical strength, stiffness and rigidity of the guide base. However, the prior attempt is not successful because the resultant mounting flange is disposed on an exterior side of the guide shoe. The mounting flange requires a large installation space provided on the exterior side of a path of travel of the chain, which will lead to enlargement of the overall size of the engine.